Thing is, why bother? The engine, running with no external mechanical load, is running an alternator that produces 12 volts (13.6V DC, actually, but who cares) and provides up to 120 Amps of current. You can use the DC to charge batteries to run equipment when you're not burning fuel running the engine. Otherwise, you hook the drive shaft to an AC generator and produce 120V AC at an amperage dependent on the capacity of the AC generator. I gather it would produce enough power to run a refrigerator/freezer. The idea opens some possibilities.Converting the 12v 120amp DC to AC 120v would give about 10 amps or slightly more than a standard home power outlet.
(quick calculation, may be + or - 10%)